docs: add Reverse Proxy on OpenShift guide (#990)

* docs: add Reverse Proxy on OpenShift guide

Add a guide for running the NetBird reverse proxy on OpenShift with the
rootless UBI image under the restricted-v2 SCC. It covers the proxy
Deployment with self-managed ACME certificates on a PVC, exposure via a
TCP LoadBalancer or TLS-passthrough Routes, wiring a backend through a
routing peer, verification, and troubleshooting.

Adds the page to the Reverse Proxy sidebar and cross-links it from the
overview and Bring Your Own Proxy pages.

* docs: simplify OpenShift proxy guide

Drop the version availability note and the amd64 node restriction since
the rootless UBI proxy image is published for both AMD64 and ARM64, and
replace the interactive token prompt with plain export statements.

* docs: restructure OpenShift proxy guide and add http-01 variation

Make the guide easier to follow for reverse proxy operators:
- Put the LoadBalancer vs passthrough Route decision and the resource
  footprint up front.
- Source the management address from the Secret and drop hardcoded
  namespaces so the manifests apply without edits.
- Add checkpoints after each step and move alternatives (cert-manager,
  replicas, upgrades, removal) into an "Operating the proxy" section.
- Document http-01 with the UBI image's :8081 challenge listener and why
  it requires the LoadBalancer exposure.

Fixes from a test deployment on OpenShift 4.17 with the PR build of the
UBI proxy image:
- Add pkgs.netbird.io (geolocation database) to the egress requirements.
- Show how to switch a pending LoadBalancer Service back to ClusterIP.
- Describe the periodic PROTOCOL_ERROR reconnect symptom of a management
  idle timeout separately from gRPC routing failures.
- Note that autocert handshake warnings during first issuance are expected.

src/components/NavigationDocs.jsx

@@ -262,6 +262,10 @@ export const docsNavigation = [
                         title: 'Bring Your Own Proxy',
                         href: '/manage/reverse-proxy/bring-your-own-proxy',
                     },
+                    {
+                        title: 'OpenShift',
+                        href: '/manage/reverse-proxy/openshift',
+                    },
                     {
                         title: 'Custom Domains',
                         href: '/manage/reverse-proxy/custom-domains',